Liquid laundry detergents have been known in the art for many decades. Modern detergents are non-phosphated and are preferably comprised of synthetic anionic surfactants in order to mitigate the effects of hard water on both the cleaning performance and the machine. However, highly anionic detergent compositions foam considerably in modern washing machines, even to the extent where cleaning efficiency is reduced due to the foam cushioning the agitation of the fabrics. Formulation strategies to reduce the sudsing of synthetic anionic laundry detergents are well known in the prior art, although much of the art relates to powdered detergents and not liquid compositions and to older phosphated and/or heavily built formulations.
For example, U.S. Pat. No. 2,954,347 (St. John et al.) discloses the addition of fatty acid mixtures to powdered anionic surfactant compositions to reduce sudsing. The '347 patent specifically states that there is no measurable decrease in cleaning efficiency from the addition of certain fatty acid mixtures to detergents comprising synthetic anionic sulfate or sulfonate surfactants. Clearly the reduction in sudsing without concomitant reduction in performance was possible in the examples within '347 because of the high levels of phosphate utilized, (a strategy possible in powdered detergents, and commonplace before environmental concerns and regulatory constraints).
U.S. Pat. No. 2,954,348 (Schwoeppe) describes adding a synergistic combination of fatty acids and nonionic surfactants to synthetic anionic detergents in order to reduce foaming and maintain performance. The compositions described in '348 are also powders and phosphated, wherein the phosphate content may help to mitigate the deleterious effects of the added fatty acids. The nonionic surfactants described in the '348 patent were the Pluronic® surfactants, many of which were not only non-foaming but also defoaming.
U.S. Pat. No. 3,707,503 (Kenny) describes the use of certain alkanolamides with a select group of saturated fatty acids for controlling the sudsing of anionic detergent compositions. These compositions are also powders and contain phosphate (for example tetrapotassium pyrophosphate) or NTA as strong chelants to counteract the hard water effects of the added fatty acids.
U.S. Pat. No. 3,892,680 (Benjamin, et al.) describes maintaining cleaning performance and/or whiteness in a non-phosphated powder composition by the combination of calcium-insensitive synthetic anionic surfactants, such as alkyl ether sulfate, alkali metal carbonate and alkali metal silicate. The formulations disclosed in '680 do not include fatty acids and the disclosure is silent on the suds levels of these compositions that are devoid of fatty acid soaps.
U.S. Pat. No. 3,929,663 (Arai, et al.) describes “controlled foaming detergent compositions” by the addition of alkyloxy- or alkyloxymethyl-fatty acids to linear alkylbenzene sulfonate detergents, however again in powdered compositions further comprising phosphate. Most interesting is the mention that “no notable foam-controlling effect, like the one obtained with ABS [referring to branched alkyl benzene sulfonate] can be obtained by adding thereto sodium stearate” ('663, Col 1, Lines 35-38). The inventors are apparently stating that ordinary straight chain fatty acids soaps are useful for controlling the sudsing in branched alkyl benzene sulfonate (ABS) containing detergents, but are not useful for controlling the suds in linear alkyl benzene sulfonate detergents. As will be described below, we believe the fatty acid soaps do modulate sudsing of linear alkyl benzene containing liquid compositions, but that the real problem to overcome is the increase in graying of fabrics.
U.S. Pat. No. 4,009,114 (Yurko) relates to non-phosphated powdered laundry detergent compositions comprising the combination of alkyl aryl sulfonate anionic surfactant (including linear alkyl benzene sulfonate), fatty acid soap, citric acid, along with carbonate and silicate in a ratio of from 4:1 to 1:4, but does not suggest the enhanced whiteness retention properties of the unique combination of surfactants involved in the present invention.
U.S. Pat. No. 4,304,680 (Wixon) discloses improvement in the performance of “laundry soap” by addition of alcohol ether sulfate along with alkali metal carbonate, alkali metal silicate, or mixtures thereof. The '680 product is predominately a fatty acid soap, with “soap curd” reducing additives that include organic solvents and minor quantities of synthetic surfactant combinations differing from the combinations used in the present invention.
U.S. Pat. No. 5,425,891 (Pujol et al.) describes the use of a combination of fatty acid soaps and ethoxylated glycerin to reduce the sudsing seen from powdered anionic detergents comprising sodium dodecylbenzene sulfonate, while maintaining or even improving cleaning performance. The examples disclosed in '891 are highly chelated with either tripolyphosphate or zeolite and also comprise enzymes. For these examples, we surmise it would be difficult to see the deleterious effects of the added fatty acid soaps or known for certain if the ethoxylated glycerin assisted performance.
With modern high-efficiency liquid detergents that are non-phosphated through environmental regulation, and necessarily not heavily built due to solubility, safety and viscosity constraints, it is well known that the addition of fatty acids to anionic detergent compositions increases the graying of fabrics. That is, there is much reduced whiteness retention when laundering white/light fabrics with detergents containing fatty acid soaps. Accordingly, liquid laundry detergent compositions that show improved whiteness retention and controlled sudsing incorporating common synthetic anionic surfactant and fatty acid soaps are heretofore unknown. There is a clear need for improved liquid laundry detergent compositions that are based on common inexpensive ingredients.
It has now been surprisingly found that the combination of fatty acids, alkyl benzene sulfonate, alcohol ether sulfate, alcohol ethoxylate, polyacrylate and most importantly silicate, provide for a low sudsing, high efficiency liquid laundry detergent with unprecedented whiteness retention. Unexpectedly, silicate has been found to mitigate the graying of fabrics commonly seen when using fatty acids soaps in anionic detergent compositions.